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Tuning Optical Properties of Re(I) Carbonyl Complexes by Modifying Push–Pull Ligands Structure

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journal contribution
posted on 07.10.2019, 19:51 by Tomasz Klemens, Anna Świtlicka, Agata Szlapa-Kula, Łukasz Łapok, Magdalena Obłoza, Mariola Siwy, Marcin Szalkowski, Sebastian Maćkowski, Marcin Libera, Ewa Schab-Balcerzak, Barbara Machura
In this work, the structure–property relationship was investigated for a series of Re­(I) carbonyls [ReCl­(CO)3(R-terpy2N)], [ReCl­(CO)3(R-dtpy2N)], and [ReCl­(CO)3(R-dppy2N)]. The studied compounds bear 2,2′:6′,2″-terpyridines (R-terpy), 2,6-di­(thiazol-2-yl)­pyridines (R-dtpy), and 2,6-di­(pyrazin-2-yl)­pyridines (R-dppy) functionalized with strongly electron-donating cyclic (piperidine and morpholine) and acyclic (dimethylamine, diphenylamine) amine donor attached to the central pyridine ring of the triimine skeleton via phenylene linkage. Their thermal properties were evaluated using DSC. The ground- and excited-state properties of these systems were elucidated with electrochemistry, absorption and emission spectroscopy, and density-functional theory (DFT)-based calculations. The terpy skeleton was found to efficiently stabilize the LUMO orbital, as manifested by the most negative reduction potentials for Re­(I) terpyridine complexes and significant blue-shift of the absorption and emission of [ReCl­(CO)3(R-terpy2N)] in relation to those of Re­(I) carbonyls bearing dtpy- and dppy-based ligands. Substitution of the triimines with amine substituents resulted in participation of intraligand charge-transfer (ILCT) transitions, and it was found to be beneficial for hole-transport properties of the Re­(I) carbonyls. The constructed nondoped and doped single layer diodes based on Re­(I) complexes emitted red light with various intensity.